Pen-type injector

ABSTRACT

A pen-type injector is improved so that a user may select a delivery dose of a medicinal product from a multidose cartridge. The injector includes a housing, a cartridge containing the medicinal product retained within the housing, a piston rod, a dose selecting member to select the dose of medicinal product to be expelled, and a drive member to expel the selected dose of the medicinal product. The housing is formed unitary so that the dose selecting member and the drive member are moveably retained within the housing. The injector may include a ratchet associated with an insert to ensure the piston rod only rotates in a single direction through the insert, a button located on the drive member, and a clutch which upon depression of the button prevents rotation between the dose selecting member and the drive member.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 13/025,852, filed Feb. 11, 2011, now U.S. Pat. No.8,888,750, which is a continuation application of U.S. patentapplication Ser. No. 10/790,025, filed Mar. 2, 2004, now U.S. Pat. No.7,905,867, and claims priority to GB Patent Application No. 0304823.8,filed Mar. 3, 2003, the entire contents of each of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to pen-type injectors, that is toinjectors of the kind that provide for administration by injection ofmedicinal products from a multidose cartridge. In particular, thepresent invention relates to such injectors where a user may set thedose.

BACKGROUND

Such injectors have application where regular injection by personswithout formal medical training occurs. This is increasingly commonamongst those having diabetes where self-treatment enables such personsto conduct effective management of their diabetes.

These circumstances set a number of requirements for pen-type injectorsof this kind The injector must be robust in construction, yet easy touse both in terms of the manipulation of the parts and understanding bya user of its operation. In the case of those with diabetes, many userswill be physically infirm and may also have impaired vision. Where theinjector is to be disposable rather than reusable, the injector shouldbe cheap to manufacture and easy to dispose of (preferably beingsuitable for recycling).

SUMMARY

It is an advantage of the present invention that an improved pen-typeinjector is provided.

According to first aspect of the present invention, a pen-type injectorcomprises a housing;

-   -   a cartridge containing medicinal product, the cartridge being        retained within the housing;    -   means for selecting a dose of medicinal product to be expelled;    -   means for expelling the selected dose of medicinal product;    -   characterised in that the housing comprises a unitary housing        within which the dose selecting means and the dose expelling        means are moveably retained.

It is an advantage of this aspect of the invention that it affords amore robust construction of a pen-type injector.

According to a second aspect of the present invention, a pen-typeinjector comprises

-   -   a piston rod having a screw thread;    -   an insert located in the housing and through which the piston        may rotate;    -   ratchet means associated with the insert to ensure the piston        only rotates in a single direction through the insert;    -   a dose dial sleeve rotatable with respect to the housing and the        insert;    -   a drive sleeve which is axially displaceable but not rotatable        with respect to the piston rod;    -   a button located on the drive sleeve and rotatable with respect        to the drive sleeve; and    -   clutch means which upon depression of the button prevents        rotation between the dose dial sleeve and the drive sleeve.

Preferably, the injector further comprises a nut rotatable with respectto the drive sleeve and axially displaceable but not rotatable withrespect to the dose dial sleeve.

Preferably, the insert comprises a web having an opening, a firstcylindrical portion extending from a first side of the web, a secondcylindrical portion extending from a second side of the web and a thirdcylindrical portion extending from a second side of the web.

Alternatively, the insert comprises a web having an opening, a firstcylindrical portion extending from a first side of the web, a bossprovided on a second side of the web and a cylindrical portion extendingaway from the web about a periphery of the boss.

In a second alternative, the insert comprises a web having an opening, afirst cylindrical portion extending from a first side of the web, a bossprovided on a second side of the web, a radial flange extending from theboss, the radial flange being spaced from the web, and a cylindricalportion extending away from the web about a periphery of the radialflange.

Preferably, the dose dial sleeve comprises a first section of firstdiameter and a second section of second diameter, the insert and aninner surface of the first section being provided with interengagingfeatures to provide a helical thread between the insert and the dosedial sleeve.

Alternatively the dose dial sleeve comprises a first cylindrical portionrigidly connected to a second generally cylindrical portion, an innersurface of the first section and an outer surface of the cylindricalportion of the insert are provided with interengaging features toprovide a helical thread between the insert and the dose dial sleeve.

More preferably, the second generally cylindrical portion comprises afirst cylindrical section and a second cylindrical section connected bya shoulder, the first section being rigidly keyed to an inner surface ofthe first portion of the dose dial sleeve, and the second section beingof the same outer diameter as the housing.

Alternatively the second generally cylindrically portion comprises afirst cylindrical section and a second cylindrical section connected bya radial flange extending from a part of the second section, the firstsection being rigidly keyed to an inner surface of the first portion ofthe dose dial sleeve, and the second section being of the same outerdiameter as the housing.

Preferably, an outer surface of the dose dial sleeve is provided withgraphics and the housing is provided with an aperture or window throughwhich a portion of the graphics may be viewed.

Preferably, the drive sleeve comprises a first part of first diameterlocated between the insert and the piston rod and a second part ofsecond diameter located between the piston rod and the dose dial sleeve,an internal surface of the drive sleeve being splined to the piston rodsuch that no relative rotation may occur between these parts, onlylongitudinal displacement.

More preferably, the central receiving area includes at a first end acentrally located domed part.

Preferably, the nut is provided on a helical thread provided on thedrive sleeve and is located between the drive sleeve and the dose dialsleeve, the dose dial sleeve and the nut being splined together byspline means to prevent relative rotation between the nut and the dosedial sleeve.

Preferably, the drive sleeve further comprises a central receiving areahaving a peripheral recess, the button being of generally “T” shapedconfiguration has a stem that is retained within the receiving area byco-operation between a peripheral bead provided on the stem retained ina peripheral recess provided in the central receiving area.

More preferably the second end of the piston rod is generally U-shaped,each of the limbs of the U-shape being received within a second part ofthe drive sleeve.

Preferably, the clutch means comprises a plurality of radially extendinglongitudinally directed teeth provided respectively on the dose dialsleeve and the drive sleeve.

Preferably, clicker means are provided between the dose dial sleeve andthe drive sleeve, the clicker means comprising a plurality oflongitudinally extending teeth and a flexible toothed member, one of theplurality of teeth and the toothed member being provided on the dosedial sleeve, the other being provided on the drive sleeve, relativerotation between the dose dial sleeve and the drive sleeve causing theflexible toothed member to ride over the teeth to produce a series ofclicks.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be described, by way of example only, withreference to the accompanying drawings, in which:

FIG. 1 shows a sectional side view of a first embodiment of an injectorin accordance with the present invention in a first position;

FIG. 2 shows a sectional side view of the injector of FIG. 1 in a secondposition;

FIG. 3 shows a sectional side view of the injector of FIG. 1 in a thirdposition;

FIG. 4 shows a sectional side view of the injector of FIG. 1 in a fourthposition;

FIG. 5 shows a sectional side view of the injector of FIG. 1 in a secondposition;

FIG. 6 shows a sectional side view of a second embodiment of an injectorin accordance with the present invention;

FIG. 7 shows a sectional side view of a third embodiment of an injectorin accordance with the present invention;

FIG. 8 shows a perspective view of a dose dial sleeve for use inconjuction with the present invention;

FIG. 9 shows a perspective view of an insert for use with the dose dialsleeve of FIG. 8; and

FIG. 10 shows a sectional side view of a fourth embodiment of aninjector in accordance with the present invention.

DETAILED DESCRIPTION

Referring first to FIGS. 1 to 5 there may be seen an injector inaccordance with a first embodiment of the present invention. Theinjector comprises a housing 2 within which are located a cartridge 4containing a medicinal product, means for setting or selecting the doseof medicinal product to be expelled and means for expelling the selecteddose of medicinal product. The housing 2 is generally cylindrical inshape and is divided into two compartments by a web 6 to be described inmore detail below. The cartridge 4 is located within a first part of thehousing 2. The dose setting means and the means for expelling theselected dose of medicinal product are retained, that is held, within asecond part of the housing 2. An advantage of a one piece housingenclosing the cartridge 4 together with the dose setting and doseexpelling means lies in the ease of assembly of the product. This is inpart due to the reduced number of components in the pen-type injector.Also, the unitary nature of the housing 2 means that the pen-typeinjector is more robust.

The cartridge 4 may be secured in position in the first part of thehousing 2 by any suitable means. A needle unit may be secured to a firstend of the cartridge 4. A temporary covering 8 is shown in this positionin the Figures. The cartridge 4 further comprises a displaceable piston10. Advancing the piston 10 towards the first end of the cartridge 4causes the medicinal product to be expelled from the cartridge 4 throughthe needle unit. A cap 12 is provided to cover the needle unit when theinjector is not in use. The cap 12 may be releaseably secured to thehousing 2 by any suitable means.

The dose setting means and the means for expelling the selected dose ofmedicinal product will now be described in more detail. The web 6dividing the housing 2 is a part of an insert 14 located within thehousing 2. The insert 14 comprises a first cylindrical portion 16extending from a first side of the web 6 and second and thirdcylindrical portions 18, 20 extending from a second side of the web 6.The web 6 is provided with a circular opening 22 extending through theweb 6.

The first cylindrical portion 16 extends from a periphery of the web 6.The insert 14 is secured to the housing 2 by way of the firstcylindrical portion 16 by any suitable means. In the illustratedembodiment features 24 are provided within the housing 2 and on an outersurface of the first cylindrical portion 16 to enable the insert to be asnap fit to the housing 2.

The second cylindrical portion 18 extends a small distance from thesecond side of the web 6 about a periphery of the opening 22. Aninternal surface of the second cylindrical portion is provided with ascrew thread 26.

The third cylindrical portion 20 extends substantially within thehousing 2 from the second side of the web 6. The diameter of the thirdcylindrical portion 20 is such that a first channel 28 is formed betweenan outer surface of the second cylindrical portion 20 and an innersurface of the third cylindrical portion. A second channel 30 is formedbetween an outer surface of the third cylindrical portion 20 and thehousing 2.

A piston rod 32 is provided extending through the opening in the web 6.The piston rod 32 is generally elongate and is provided with a screwthread 34 extending from a first end of the piston rod 32. The screwthread 34 of the piston rod 32 engages the screw thread of the innersurface of the second cylindrical portion 18 of the insert 14. The firstend of the piston rod 32 is provided with a pressure foot 36. In use thepressure foot 36 is disposed on the first side of the web 6 to abut thecartridge piston 10.

Ratchet means 40 are located adjacent the web 6 on the first side of theweb 6. The ratchet means 40 serve the purpose of allowing the piston rod32 only to rotate through the insert 14 in a single direction. Due tothe one piece construction of the housing, the ratchet means can be madelarger than in known devices and so is stronger (more rigid).

A dose dial sleeve 50 of generally cylindrical form comprises a firstsection of first diameter and a second section of second diameter. Thefirst section is located within the second channel 30. An inner surfaceof the first section and the outer surface of the third cylindricalportion 20 are provided with interengaging features to provide a helicalthread 52 between the insert 14 and the dose dial sleeve 50.Conveniently as in The illustrated embodiment, this is achieved by ahelical track provided on the outer surface of the third cylindricalportion 20 within which a helical rib provided on the inner surface ofthe dose dial sleeve 50 may run. This enables the dose dial sleeve 50 torotate about and along the third cylindrical portion 20 of the insert14.

An outer surface of the first section of the dose dial sleeve 50 isprovided with graphics 53. The graphics are typically a sequence ofreference numerals. The housing 2 is provided with an aperture or window54 through which a portion of the graphics, representing a dosage valueselected by the user, may be viewed.

The graphics 53 may be applied to the dose dial sleeve 50 by anysuitable means in the illustrated embodiment, the graphics 53 areprovided in the form of a printed label encircling the dose dial sleeve50. Alternatively the graphics may take the form of a marked sleeveclipped to the dose dial sleeve 50. The graphics may be marked in anysuitable manner, for example by laser marking

It is an advantage of this arrangement that the helical thread 52 isformed within the dose dial sleeve between the dose dial sleeve and theinsert. As can be seen this means there is no direct route from outsidethe injector to the working surfaces of the helical thread. Should dustor dirt enter the pen this will tend to occur between the housing andthe dose dial sleeve where there are no working parts with which tointerfere. This is not the case for known devices in which a helicalthread is formed between the housing and an interior moving surface. Inaddition because of the narrower diameter of the helical thread 52formed between the dose dial sleeve and the drive sleeve in comparisonto a similar thread formed between the housing and the dose dial sleeve,the helical thread 52 is more efficient and easier to overhaul. Thisarrangement also produces an improvement in the dose size that can bedelivered for a particular linear travel of the dose expelling means.

The second section of the dose dial sleeve 50 is preferably of the sameouter diameter as the housing 2. Within the dose dial sleeve 50 there isa shoulder 56 between the first section of the dose dial sleeve 50 andthe second section of the dose dial sleeve 50.

A drive sleeve 60 of generally cylindrical form comprises a first partof first diameter and a second part of second diameter. A first end ofthe first part is located within the first channel 28 of the insert 14in the position shown in FIG. 1. The first part of the drive sleeve 60may be considered as comprising a first portion aligned with a secondportion. More generally in the position shown in FIG. 1 the firstportion of the drive sleeve 60 is located between the insert 14 and thepiston rod 32 while the second portion is located between the piston rod32 and the dose dial sleeve 60.

A second end of the piston rod 32 and an internal surface of the drivesleeve 60 are splined together such that no relative rotation may occurbetween these parts, only longitudinal displacement.

The outer surface of the second portion of the first part of the drivesleeve 60 is provided with a helical thread 62. A nut 64 is provided onthe helical thread 62 between the drive sleeve 60 and the dose dialsleeve 50. The dose dial sleeve 50 and the nut 64 are splined togetherby spline means to prevent relative rotation between the nut 64 and thedose dial sleeve 50.

The second part of the drive sleeve 60 is of larger diameter than thefirst part of the drive sleeve 60. There is a step 66 between the firstpart of the drive sleeve 60 and the second part. The second part of thedrive sleeve 60 is seated within the second section of the dose dialsleeve 50. The shoulder 56 of the dose dial sleeve 50 and the step 66 ofthe drive sleeve 60 are adapted to be releasably engagable with oneanother to form a clutch means. When, as in FIG. 1, the dose dial sleeve50 and the drive sleeve 60 are not in engagement the dose dial sleeve 50is able to rotate with respect to the drive sleeve 60. Conveniently, theclutch means 250 comprises a plurality of radially extendinglongitudinally directed teeth 251 provided respectively on the shoulder56 of the dose dial sleeve 50 and the step 66 of the drive sleeve 60.(see FIGS. 1 & 2). When the dose dial sleeve 50 and the drive sleeve 60are not forced together the respective teeth will ride over one another.Preferably, the radial separation of the respective teeth corresponds toa unit dosage.

The second part of the drive sleeve 60 further comprises a centralreceiving area 68 having a peripheral recess. A button 70 of generally“T” shaped configuration is provided, the stem of which is retainedwithin the receiving area. The stem of the button 70 is provided with aperipheral bead 71 that is retained in the peripheral recess, the button70 being able freely to rotate with respect to the drive sleeve 60, butbeing retained axially therewith.

Clicker means are provided between the second section of the dose dialsleeve 50 and the second part of the drive sleeve 60. In the illustratedembodiment, the internal surface of the second section of the dose dialsleeve 50 is provided with a plurality of longitudinally extendingteeth. The radial separation of the teeth preferably corresponds to aunit dosage. The second part of the drive sleeve 60 carries a flexibletoothed member 72. Relative rotation between the dose dial sleeve 50 andthe drive sleeve 60 will cause the flexible toothed member 72 to rideover the teeth to produce a series of clicks.

In FIG. 1, the injector is provided with a filled cartridge 4. Tooperate the injector a user must first select a dose. To set a dose thedose dial sleeve 50 is rotated by manipulating the second section of thedose dial sleeve 50 with respect to the housing 2 until the desired dosevalue is visible through the window 54. This action draws the dose dialsleeve 50 along the second cylindrical portion of the insert 14. Thedrive sleeve 60 cannot rotate since it is splined to the piston rod 32.The piston rod 32 does not rotate due to the action of the ratchet means40. The drive sleeve 60 is carried away from the web 6 along the pistonrod 32 by the dose dial sleeve 50 as the dose dial sleeve 50 moves outfrom the housing 2. The relative rotation between the dose dial sleeve50 and the drive sleeve 60 causes the flexible toothed member 72 to rideover the ridges in the drive sleeve 60 to create a series of clicks.This is an audible confirmation of the dose being dialed.

Since the nut 64 is splined to the dose dial sleeve 50, the relativerotation between the dose dial sleeve 50 and the drive sleeve 60 causesthe nut 64 to process along the helical thread 62 of the drive sleeve60.

Once a desired dose has been set (as shown for example in FIG. 2), todeliver the dose the user depresses the button 70 to urge the button 70towards the first end of the housing 2. When the button 70 is depressedthe second part of the drive sleeve 60 is driven into the second sectionof the dose dial sleeve 50 to engage the clutch means therebetween toprevent relative rotation between the dose dial sleeve 50 and the drivesleeve 60. The drive sleeve 60 may still rotate with respect to thebutton 70. Further longitudinal movement of the button 70 causes thedose dial sleeve 50 (together with the drive sleeve 60) to rotatetowards the first end of the injector. Since the piston rod 32 issplined to the drive sleeve 60, the piston rod 32 is also rotatedthrough the insert 14 and the ratchet means 40 towards the first end ofthe injector, thereby to advance the cartridge piston 10 and expel thedesired dose of medicinal product. The piston rod 32 continues toadvance until the drive sleeve 60 and dose dial sleeve 50 have returnedto their initial positions (FIG. 3).

It can be seen that the dose selecting means and the dose expellingmeans extend beyond a second end of the housing 2 as the dose isselected and are returned within the housing 2 as the selected dose isexpelled.

Further dosages may be delivered as required. FIG. 4 shows an example ofa subsequently selected dosage. It will be noted that the nut 64 hasadvanced further along the helical thread 62 of the drive sleeve 60. Theposition of the nut 64 along the helical thread 62 corresponds to theamount of medicinal product remaining in the cartridge 4, such that whenthe nut 64 reaches the end of the helical thread 62 (in the illustratedembodiment adjacent to the step 66 of the drive sleeve 60) and canrotate no further this corresponds to no medicinal product remaining inthe cartridge 4. It will be seen that if a user seeks to select aquantity of medical product greater than that remaining in the cartridge4, this cannot be done since when the nut 64 stops rotating the dosedial sleeve 50 and the drive sleeve 60 will become locked togetherpreventing rotation of the dose dial sleeve 50 and setting of a largerdose. FIG. 5 shows an injector according to the present invention inwhich the entire medical product within the cartridge 4 has beenexpelled.

A second embodiment of the present invention is disclosed in FIG. 6.Like reference numerals are used to refer to like parts as between thefirst and second embodiments.

The piston rod 32′ shown in FIG. 6 has a dual start thread. The pistonfoot 36′ is reversible. This has advantages in manufacture. As can beseen the structure of the insert 14′ has been revised. The first side ofthe web 6′ is substantially unchanged. The other side of the web is nowprovided with a boss 80. A cylindrical portion 20′ extends away from theweb 6′ about a periphery of the boss 80. Threaded opening 22′ extendsthrough the web 6′ and the boss 80. An end of the cylindrical portion20′ of the insert 14′ remote from the web 6′ is provided with a stop inthe form of a land 104.

The dose dial sleeve 50′ is of modified construction. The dose dialsleeve comprises a first cylindrical portion 84 rigidly connected to asecond generally cylindrical portion 86. An inner surface of the firstcylindrical portion 84 and the outer surface of the cylindrical portion20′ of the insert 14′ are provided with interengaging features toprovide a helical thread 52′ between the insert 14′ and the dose dialsleeve 50′. An outer surface of the first cylindrical portion 84 isprovided with the dose graphics. The housing 2′ is provided with anaperture or window 54′ through which a portion of the graphics may beviewed.

The second generally cylindrical portion 86 comprises a firstcylindrical section 88 and a second cylindrical section 90. The firstsection 88 is rigidly keyed to an inner surface of the first portion 84of the dose dial sleeve 50′. The second section 90 is preferably of thesame outer diameter as the housing 2′. Within the dose dial sleeve 50′there is a shoulder 56′ between the first section 86 and the secondsection 90.

A nut 64′ is provided on the helical thread 62′ between the drive sleeve60′ and the first cylindrical section 88 of the dose dial sleeve 50′.The first cylindrical section 88 and the nut 64′ are splined together byspline means to prevent relative rotation between the nut 64′ and thedose dial sleeve 50′.

The shoulder 56′ of the dose dial sleeve 50 and a step 66′ of a drivesleeve 60′ are adapted to be releasably engagable with one another toform a clutch means. When, as in FIG. 6, the dose dial sleeve 50′ andthe drive sleeve 60′ are not in engagement the dose dial sleeve 50′ isable to rotate with respect to the drive sleeve 60′. Conveniently, theclutch means comprises a plurality of radially extending longitudinallydirected teeth provided respectively on the shoulder 56′ of the dosedial sleeve 50′ and the step 66′ of the drive sleeve 60′. When the dosedial sleeve 50′ and the drive sleeve 60′ are not forced together therespective teeth will ride over one another.

It will be seen that the structure of the drive sleeve 60′ has also beenmodified. The second end of the piston rod 32′ is provided with ascooped surface within which a domed part 90 of the drive sleeve 60′ mayextend. The domed part 90 is centrally located within a second part ofthe drive sleeve 60′ at a first end of the receiving area.

The button 70′ is of generally “T” shaped configuration. The stem of thebutton 70′ is retained within the receiving area. The stem of the button70′ is provided with a peripheral bead 71′ that is retained in theperipheral recess, the button 70′ being able freely to rotate withrespect to the drive sleeve 60′, but being retained axially therewith.

When the button 70′ is depressed the drive sleeve 60′ is urged intocontact with the dose dial sleeve 50′ such that the clutch means areengaged. At the same time, the scooped surface of the piston rod 32′ andthe domed surface of the drive sleeve approach but do not contact oneanother. The advantage of this structure is that it enables the overalllength of the device to be reduced thereby enabling easier operation ofthe device when expressing fluid from a cartridge.

A further embodiment of the button 70″ and the dose dial sleeve 50″ canbe seen in FIG. 7. Again like reference numerals are used to refer tolike parts. In the embodiment of FIG. 7, the overall length of thedevice may be reduced still further. The second end of the piston rod32″ is generally U-shaped. The limbs of the U-shape are received withina second part of the drive sleeve 60″. A central receiving area of thedrive sleeve 60″ is defined by limbs located in use between the limbsformed on the second end of the piston rod 32″. The button 70″ is ofgenerally “T” shaped configuration. The stem of the button 70″ isretained within the receiving area. The stem of the button 70″ isprovided with a peripheral bead 71″ that is retained in the peripheralrecess, the button 70″ being able freely to rotate with respect to thedrive sleeve 60″, but being retained axially therewith.

The second generally cylindrically portion 86″ of the dose dial sleeve50″ comprises a first cylindrical section 88″ and a second cylindricalsection 90″ connected by a radial flange 92 extending from a part of thesecond section, the first section 88″ being rigidly keyed to an innersurface of the first portion 84″ of the dose dial sleeve 50″, and thesecond section 90″ being of the same outer diameter as the housing 2″.

In each of FIGS. 6 and 7, there is a further modification to each of thedose dial sleeve and the insert. This may be seen more clearly withreference to FIGS. 8 and 9.

At a first end of the dose dial sleeve there is located on an internalsurface a radially directed lug 100 extending generally parallel to alongitudinal axis of the sleeve. At a second end of the insert on anexternal surface thereof there is provided a catch means. The catchmeans comprises a groove 102 extending about a central land 104. Thecentral land 104 is generally wedge shaped such that a first edge 106nearer the start of the thread extends radially less far than a secondopposite edge 108 located further along the thread. A sloping surface110 is defined between the first edge 106 and the second edge 108. Thus,when the dose dial sleeve is assembled to the insert, by threading thedose dial sleeve onto the insert, the lug 100 passes over the first edge106 and over the sloping surface 110. As the lug 100 passes fully overthe land 104 some elastic deformation of the respective elements, thedose dial sleeve and the insert occurs. Once the lug 100 is over theland 104, the second edge 108 of the land 104 acts as a stop to preventremoval of the dose dial sleeve from the insert.

The location of the second edge 108 of the land 104 is convenientlychosen at a radial location corresponding to 80 units of medicinalproduct, that is the maximum dose available is 80 units when the dosedial sleeve is wound from the initial position shown in any of FIG. 1, 6or 7 to a fully extended position with the second edge 108 of the land104 contacting the lug 100.

A fourth embodiment of the present invention is disclosed in FIG. 10.Like reference numerals are used to refer to like parts.

As can be seen the structure of the insert 14″′ has been revised. Thefirst side of the web 6″′ is substantially unchanged. The other side ofthe web is now provided with a boss 80″′. A radial flange 112 extendsoutwardly from the boss 80″′, the radial flange 112 being spaced fromthe web 6″′, and a cylindrical portion 20″′ extending away from the web6″′ about a periphery of the radial flange 110. A threaded opening 22″′extends through the web 6″′ and the boss 80″′.

The dose dial sleeve 50″′ is of modified construction. The dose dialsleeve 50″′ comprises a first cylindrical portion 84″′ rigidly connectedto a second generally cylindrical portion 86″′. An inner surface of thefirst portion 84″′ and the outer surface of the cylindrical portion 20″′of the insert 14″′ are provided with interengaging features to provide ahelical thread 52″′ between the insert 14″′ and the dose dial sleeve50″′. An outer surface of the first cylindrical portion 84″′ is providedwith the dose graphics. The housing 2″′ is provided with an aperture orwindow 54″′ through which a portion of the graphics may be viewed.

The second generally cylindrical portion 86″′ comprises a first innercylindrical section 88″′ and a second outer cylindrical section 90″′.The first section 88″′ is rigidly keyed to an inner surface of the firstportion 84″′ of the dose dial sleeve 50″′. The second section 90″′ ispreferably of the same outer diameter as the housing 2″′. Within thedose dial sleeve 50″′ there is a radial flange 94 extending between theouter section 90″′ and an intermediate part of the inner section 88″.

A nut 64″′ is provided on a helical thread 62″′ formed on the drivesleeve 60″′. The nut 64″′ is disposed between the drive sleeve 60″′ andthe second cylindrical section 88″′ of the dose dial sleeve 50″′. Thesecond cylindrical section 88″′ and the nut 64″′ are keyed together byspline means to prevent relative rotation between the nut 64″′ and thedose dial sleeve 50″′.

An upper surface of the radial flange 94 Of the dose dial sleeve 50″′and a step 66″′ of the drive sleeve 60″′ are adapted to be releasablyengagable with one another to form a clutch means. When, as in FIG. 10,the dose dial sleeve 50″′ and the drive sleeve 60″′ are not inengagement the dose dial sleeve 50″′ is able to rotate with respect tothe drive sleeve 60″′. Conveniently, the clutch means comprises aplurality of radially extending longitudinally directed teeth providedrespectively on the radial flange 94 of the dose dial sleeve 50″′ andthe step 66″′ of the drive sleeve 60″′. When the dose dial sleeve 50″′and the drive sleeve 60″′ are not forced together the respective teethwill ride over one another.

The invention claimed is:
 1. A drive mechanism for use in a drugdelivery device comprising: a housing; a dose dial sleeve located in thehousing and having a helical track configured to allow the dose dialsleeve to rotate and translate relative to the housing during dosesetting and dose delivery; a drive sleeve releasably connected to thedose dial sleeve and comprising a central receiving area; a piston rodextending through a threaded circular opening in the housing, where thepiston rod has a first end and a second end, where the first endcomprises a thread, the second end having a larger diameter than thefirst end and comprises a U-shaped cross-section having limbs extendinglongitudinally in a proximal direction, where the limbs are receivedwithin the drive sleeve; and a button of a generally T-shapedconfiguration comprising a stem provided with a peripheral bead, whereinthe stem of the button is retained within the central receiving areawith the peripheral bead being retained in a peripheral recess of thedrive sleeve, wherein the button is able to freely rotate with respectto the drive sleeve.
 2. The drive mechanism of claim 1 where a pressurefoot is attached to the first end of the piston rod on a first side of aweb.
 3. The drive mechanism of claim 2 where the pressure foot isreversible.
 4. The drive mechanism of claim 1 where a clicker isprovided between the dose dial sleeve and the drive sleeve.
 5. The drivemechanism of claim 1 where the piston rod has a dual start thread. 6.The drive mechanism of claim 1 further comprising a clutch comprising aplurality of radially extending longitudinally directed teeth, where aradial separation of the teeth corresponds to a unit dose of a medicinalproduct, where the clutch is configured to releasably and rotationallyfix together the dose dial sleeve and the drive sleeve.
 7. The drivemechanism of claim 1, wherein the first end extends through a circularopening in a web that is located in the housing.
 8. The drive mechanismof claim 1 where the second end of the piston rod is configured toengage an internal surface of the drive sleeve.